The present invention relates generally to the field of spectroscopy and more particularly to an apparatus for use in obtaining high resolution spectral and temporal information simultaneously of an ultrafast pulse of luminescent light on a 10.sup.-14 to 10.sup.-2 second time scale.
The study of picosecond luminescence phenomenon requires an instrument which simultaneously measures both spectral as well as temporal information.
It is well known that one can obtain intensity versus wavelength information of a light pulse using a spectrograph. It is also well known that one can obtain intensity versus time information of a light pulse using a streak camera.
Spectrographs are old in the art and have been in use for over 50 years. Streak cameras are about ten years old in the art and are used principally to directly measure the time dynamics of luminous events. A typical streak camera comprises an entrance slit which is usually rectangular, relay optics, a streak tube and appropriate sweep electronics. The streak tube contains a photocathode on the front, accelerating and sweeping electrodes and an output phosphor screen on the back. The relay optics serve to image the entrance slit onto the photocathode. The output streaked image is typically recorded using photographic film or video type readout systems. In an article entitled "An Ultrafast Streak Camera System" by N. H. Schiller, Y. Tsuchiya, E. Inuzuka, Y. Suzuki, K. Kinoshita, K. Kamiya, H. Iida and R. R. Alfano appearing in the June, 1980, Edition of Optical Spectra, various known streak camera systems are discussed. The article is incorporated herein by reference.
In the past, to spectrally resolve the kinetics of different emission components of a luminous event, a filter or spectrograph has been positioned in front of the entrance slit of the streak camera. This arrangement for obtaining spectral as well as temporal information simultaneously, has many limitations. Some of these limitations are as follows:
1. Limited spectral range covered; PA0 2. Wide bandwidths about discrete wavelengths; PA0 3. Non-continuous wavelength display; PA0 4. Achromatic aberrations caused by the relay lens; PA0 5. Limited spectral coverage requiring changing of relay optics; PA0 6. Refocusing of input optics over well-defined spectral regions due to achromatic aberrations through relay lenses; and PA0 7. Limited spectral transmission of relay optics. PA0 1. It is not compact in size; PA0 2. It involves rotating the grating by 90.degree. from its normal orientation in a spectrograph relative to the streak camera; PA0 3. It involves tilting the spectrograph body by 23.degree. relative to the streak camera tube; PA0 4. It is limited to spectral resolution of about 200.ANG., PA0 5. It involves repositioning and alignment of the spectrograph portion of the apparatus and realignment of the collection optics each time the wavelength region to be examined is changed, and PA0 6. It requires a flexible, non-rigid light tight shroud between the spectrograph and the streak camera.
In an article by G. W. Robinson, T. A. Caughey, R. A. Auerback and P. J. Harman entitled: "Coupling An Ultraviolet Spectrograph To A SC/OMA For Three Dimensional (n,I,t) Picosecond Fluorescence Measurements" appearing in Multi-Channel Image Detectors pp. 199-213, ACS Symposium Series 102, American Chemical Society, there is described an apparatus wherein a spectrograph is coupled to a streak camera in order to eliminate some of the above noted problems. The system employs an entrance slit 1000 microns high by 50 microns wide. Some of the shortcomings of the apparatus described in the article are:
In an article entitled "Picosecond Characteristics Of A Spectrograph Measured By A Streak Camera/Video Readout System" by N. H. Schiller and R. R. Alfano appearing in Optical Communications, Volume 35, number 3, pp. 451-454, 1980 which article is incorporate herein by reference, the problem of time broadening which may result from using spectroscopic instruments to measure picosecond luminous events is discussed.
In U.S. Pat. No. 4,162,851 there is disclosed a photometering method for multi-dimensional measurements wherein selected wavelengths of light are projected on a sample to permit three dimensional plots of a spectrum over a period of time to be obtained. In U.S. Pat. No. 3,765,769 there is described a device for producing a dynamic spectrogram and a technique for recording the component wavelengths and their relative intensity as a function of time. In U.S. Pat. No. 4,320,971 there is described a spectrophotometer operable to obtain a photoelectrical conversion signal corresponding to an arbitrarily selected wavelength from the signal time-sequentially produced from a one-dimensional image sensor. In U.S. Pat. No. 4,299,488 there is disclosed to a time-division multiplexed spectrometer operable to convert the output from a radiation source into a time-space and wavelength-division multiplexed pulse train. In U.S. Pat. No. 4,060,327 there is disclosed a spectrophotometer for receiving light from a test sample and measuring the radiant thereof as a function of wavelength, with the device providing outputs proportional to the intensity of the light rays at the different wavelengths received thereby. Other known patents relating to spectroscopy in general include U.S. Pat. Nos. 2,436,104, 2,823,577 and 3,385,160.
It is an object of this invention to provide a new and improved temporal spectral photometer.
It is another object of this invention to provide a temporal spectral photometer for use in obtaining spectral and temporal information simultaneously of an ultrafast pulse of luminescent light.
It is still another object of this invention to provide a temporal spectral photometer as described above which is compact and which provides spectral resolution of better than 10 .ANG. and time resolution of better than about 10 ps.
It is a further object of this invention to provide a temporal spectral photometer as described above on which the spectrograph portion of the instrument is not tilted or rotated relative to the streak camera portion of the instrument and which does not require repositioning or realignment for different angular positions of the light dispersing element.
It is another object of this invention to provide a temporal spectral photometer or described above in which the spectrograph and streak camera portions may be enclosed in a non-flexible type housing.
It is a further object of this invention to provide an improved and novel arrangement for coupling a spectrograph to a streak camera.
It is still a further object of this invention to provide a temporal spectral photometer which includes an arrangement for aligning the entrance slit with the incoming light on a luminous sample.
It is another object of this invention to provide a temporal spectral photometer which includes an arrangement for aligning a streak camera with relay optics with incoming light on a luminous sample.